The wet stage of the coffee is one of the most used processes for coffee growers to carry out the transformation of the cherry coffee into dry parchment, since it enables the obtainment of a bean of high physical quality. Said process comprises basically the following steps: 1) selective or non selective coffee harvesting, 2) classification of the coffee into cherry, 3) depulping, 4) demucilaging process, 5) washing, and 6) drying.
Demucilaging is a process by means of which it is eliminated the mucilage coating the endocarp or parchment of the bean and that is exposed after carrying out the depulping process. Said mucilage is highly hygroscopic and pectin rich, and for this reason its presence is an obstacle for drying and preserving the beans.
The processes currently known for removing mucilage from coffee beans include biochemical demucilaging, chemical demucilaging and mechanical demucilaging.
Biochemical or fermentation actions are based on the solubilization of the mucilage due to decomposition of pectins through soluble ferments or diastases that normally exist in the mature coffee and that act as catalysts able to solubilize all the pectin material. In addition, microbial fermentation indirectly exerts a favorable action on mucilage solubilization because it is generally accompanied by an increase in the temperature, fact that increases the diastases action.
Unfortunately, the demucilaging methods made by fermentation of the depulped bean are related to high costs on the ecological level—due to the use of abundant water in the process, which is further poured into rivers—, and on the economical level,—since the fermentation process reduces the weight and quality of the bean—.
On the other hand, chemical demucilaging comprises the use of products such as sodium, potassium or calcium hydroxide, which properly dosed are applied to depulped coffee stacks to carry out a process of alkaline hydrolysis. However, coffee undergoing chemical demucilage is characterized by being less acid compared to those treated through natural fermentation.
Now, mechanical demucilage implies detachment of mucilage basically as a consequence of friction between beans or high pressure water application. Therefore, for example, in the state of the art, some processes where mucilage is detached through friction caused by mixing depulped coffee with sand or sawdust are known (Urgelles, 1912), and also devices using big amounts of pressurized water as a mechanism for demucilaging depulped coffee beans, are known (Pellas and Kraunt, 1941).
On the other hand, researchers of the Agricultural Experiment Station in Hawaii have considered mechanical demucilage from 1953. Specifically, during 1957 they published an article1 where they described a demucilaging apparatus consisting essentially of a U shaped tube and a series of internal vanes, that functions considering that the specific weight of depulped coffee is slightly superior to that of water and therefore the water flow inside said tube drags coffee, as long as the flow speed is not excessively slow. 1Fukunaga, E. T.; A new mechanical coffee demucilaging machine; Bulletin—Hawaii Agricultural Experiment Station (EUA); December 1957 (No 115) 18 p.
According to what is disclosed by Fukunaga et al., once the vanes are functioning, the freshly depulped coffee starts to tack on the feeding tube together with a carefully regulated water flow, in a manner that when the coffee level rises in the feeding tube, also rises in the mixing tube (communicating vessels principle) and while the coffee mass flows through the entire tube, mucilage is detached from the almond by fast rotation of the vanes. Finally, demucilaged coffee is poured by the exit hopper and is conducted to a vibrating sieve to wash demucilaged coffee almonds through the application of clean water.
Now, in the state of the art demucilaging machines are known, as the one disclosed by Álvaro Ardila Duarte2 in 1995, which is constituted by four systems or subsets working simultaneously and progressively in vertical position to seize gravity force during the mucilage separation process. 2Vertical demucilaging and washing machine for coffee; Invention Patent granted to Álvaro Ardila Duarte. Filing date: Jul. 14, 1995.
Said machine comprises a vertical rotor having in the middle part some steel extensions or fingers, which coincide with the position of the polygonal basket that is part of the demucilating machine, and by rotation they generate shear and tension forces that provoke the separation of mucilage and impurities from coffee beans. Sides and edges of the rods forming the polygon of the polygonal basket avoid that the coffee mass spins at the same speed that one of the vertical rotor, while the pressure and compression forces that the coffee beans undergo because of the rotor and the vertical polygonal basket make that mucilage and impurities that are being detached from coffee are exiting by the vertical slots of the polygonal basket.
However, the mechanical design of the previously described demucilating machine does not allow to efficiently graduate the washing intensity of the beans, that is critical during coffee demucilaging because of the differences in the viscosity and adherence of mucilage to bean according to the coffee variety, the time between harvest and the percentage of mature coffee cherries treated. In addition, the vertical position of the rods forming the polygonal basket of said machine has demonstrated to be unsuitable for achieving an effective evacuation of mucilage and impurities that are detached from the coffee grains, while the geometry and disposition of the metallic basket do not allow efficient removal of mucilage.
On the other hand, on 1996 Adelcio Piagentini3 disclosed a demucilaging machine constituted by a cylinder located in vertical or slanting position with an inner grid forming a chamber wherein a rotor is spinning with it in a concentric manner, said rotor located in the lower part—which is the feeding area of the machine—a helix causing the ascending movement of the product generating compression between the beans due to the own weight of the product accumulated at the final part of the rotor as a consequence of the vertical or slanting position of the shaft of the apparatus. The water radially injected, along with the stirring induced by the tabs at the final part of the rotor causes the removal and washing of mucilage from the beans that leave the upper part of the cylinder and are already demucilaged. 3Ecological vertical demucilaging machine with ascending flow; Adelcio Piagentini; Invention Patent; Filing date: Jun. 20, 1996
Unfortunately, said equipment uses a grid of perforated foil for the exit of the mucilage and impurities, which is inefficient because of the multiple blockages that said arrangement generates. Likewise, the design of the demucilating machine disclosed by Piagentini does not enable the adjustment of the washing intensity of the coffee beans, while the geometry and arrangement of the metal basket do not allow achieving an efficient removal of mucilage.
Because of the above, it is absolutely clear that there is still a need for designing demucilating machines that allow overcoming the technical obstacles shown by the apparatus that is part of the current state of the art, and that therefore allow carrying out a demucilaging, cleaning and washing process for the depulped coffee beans in an efficient manner, that is to say, with a lower use of water and power.